1,720,972 research outputs found
PHOSPHATE ORE PRE-REACTION WITH ACIDIC PROCESS WATER
No full textThis study evaluated the use of phospho-gypsum pond water to pre-react phosphate ore associated with phosphoric acid production via the wet process. The objective was to improve phosphate recovery and aid in the management of pond water inventory. The non-catalytic heterogeneous solid-liquid reaction kinetics were examined associated with carbonate in the ore and the acidic phosphate, fluoride and sulfate present in pond water. Additionally, the sedimentation and dewatering characteristics of phosphate ore slurry were evaluated to determine the feasibility of recovering neutralized pond water and returning ore slurry back to an acceptable solids concentration ready for acidulation with sulfuric acid. The reaction kinetics between acidic process water and phosphate ore exhibited zero and first order reaction behavior and Arrhenius temperature dependence. Additionally a mixture of hydro-cyclones, gravity thickening and centrifugation proved to be feasible options for separating neutralized process water effluent and re-concentrating phosphate ore slurry.Thesis (M.S., Chemical and Materials Science Engineering) -- University of Idaho, 201
Dynamic Adsorption Studies of Organic Iodine Species on Mordenites
No full textOff – gas stream from used nuclear fuel recycling operations comprises of various contaminants such as 3H, 14C, 85Kr, 131I, and 129I. Radioactive iodine, 129I, is of significant concern due to its tendency to form hard-to-capture toxic volatile organic compounds such as methyl iodide, half-life in excess of 15 million years, and tendency to accumulate in human thyroid glands. It also has adverse impacts on the environment due to its toxic nature. Organic iodides can be hazardous even at ppb level concentrations, and hence the capture of 129I is extremely important. Various methods such as absorption and adsorption have been employed in the past to capture volatile iodine species. Recent studies have been focusing on the adsorption of iodine species using solid porous adsorbents, and the current work involves the capture of organic iodine species on mordenites. The off-gas environment was simulated using ppb level concentration of iodine species and the dynamic adsorption experiments were conducted to determine the efficiency of mordenites as adsorbents. Three different mordenites - sodium mordenite, partially exchanged silver mordenite, and fully exchanged silver mordenite were used as adsorbents. The silver mordenites were synthesized by ion exchange between silver nitrate solution and sodium mordenite and subjected to structural and compositional analysis. Adsorption-desorption cycles at different temperatures and using different materials of construction for the column were conducted and the effect of silver content on the adsorption capacity of sorbents was determined. The sorption columns exhibited behavior atypical of pure adsorption with no breakthrough and exhaustion of the adsorbents. It was hypothesized columns were behaving as reactors operating at a steady-state. Kinetic analysis of the system was conducted incorporating the effects of diffusion and mass transfer. The analysis indicates that a second-order reaction was the rate-controlling mechanism for methyl iodide removal. These research findings could give good insights about the behavior of volatile organic iodine species at lower concentrations and their effective capture.masters, M.S., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 2020-1
Isolation of electrode performance issues for lithium ion batteries during calendar and cycle life
No full textIn an effort to reduce fuel consumption by improving vehicle efficiency, several automakers have offered electrified vehicles options to consumers. Development, testing, in-depth failure analysis and modeling of lithium ion battery technology are critical for the continued development and growth of the electrified vehicle market. In this work, lithium ion cells were cycle and calendar aged under various conditions, such as temperature and state of charge, to identify capacity fade, resistance rise and power fade associated with the Plug-In Hybrid Vehicle (PHEV) usage scenarios. A reference electrode was inserted to several cells to separate the electrode performance from the cell performance. The testing results were modeled to estimate life for the cells at common operating temperatures.
Focused destructive analyses were performed with half-cell testing utilizing a lithium reference electrode to understand the mechanisms that affect power, energy, resistance and capacity fade in the path dependence studies of commercial Lithium Ion cell testing. The reference electrode is used to investigate voltage characteristics of the individual electrodes throughout calendar (i.e., zero current) and current cycle-ageing regimes. The response of the electrode voltages (vs. reference) to a given current pulse prior to and during interruptions of the aging regime indicates that the resistance of the positive-electrode is much larger than that of the negative electrode.
Modeling of the calendar and cycle life testing results using an Arrhenius based semi-empirical model was demonstrated for temperature and state of charge accelerated calendar and cycle life testing. Calendar life estimation has become critical for the continued development of electrified vehicles and the warranties associated with them. A methodology is presented that can be used to characterize the performance degradation of cells for use in automotive applications.
Battery manufacturers, by understanding the factors that limit life and which electrode limits cell performance over life can improve cell technology: life, performance, and cost. Battery advancements will be accompanied by reduced petroleum consumption, which will facilitate the acceptance of electrified vehicles that will be competitive at the same cost and performance level in a market dominated by gasoline engines.Thesis (Ph.D., Chemical and Materials Science Engineering) -- University of Idaho, 201
Separation of Adjacent Rare Earth Elements Using Solvent Extraction
No full textIndustrial rare earth separation facilities utilize the phosphonic acid PC88A for solvent extraction processes. Separation of adjacent lanthanides using solvent extraction is especially costly and difficult due to their chemical similarities. Process improvements provide significant positive impacts on regulatory and economic challenges associated with these difficult separations.
The separation of praseodymium and neodymium has been of particular interest recently due to current and forecasted future demand for high purity neodymium. Laboratory solvent extraction testing combined with MATLAB modeling has been used to develop and test solvent extraction flowsheets to separate high purity neodymium from a 25 wt % praseodymium and 75 wt % neodymium mixture . The flowsheet chemistry is based on the current industrial extractant, PC88A. Mixer settler flowsheet testing with PC88A has shown that greater than 99% purity neodymium can be produced with a neodymium scrub solution in a 12-stage scrubbing circuit.
An overall flowsheet concept has been designed, tested, and evaluated to simultaneously produce didymium and high purity neodymium. The methods and processes developed in this research can be applied to all of the rare earth elements (REE) in the lanthanide series to develop a modeling capability for complex separation schemes. Additionally, the modeling principles can be applied to alternative solvent systems for REE separations. The methods presented for flowsheet development and optimization provide a design capability that supports a viable domestic supply of critical materials.Thesis (M.S., Chemical and Materials Science Engineering) -- University of Idaho, 201
The Effect of Impurities and Geometry on the Corrosion and Thermodynamic Behavior of Molten Salts
No full textMolten salt systems are highly relevant to the energy industry and have become a focus of much research in recent years, particularly in nuclear energy and thermal energy storage. Many types of molten salt are used for various systems, including fluoride, chloride, and nitrate salts. These types of salts have thermodynamic and chemical properties, which make them advantageous to energy production systems. Molten salt systems are superior to other systems in many ways, including design simplification, atmospheric operating pressures, higher heat capacities, safer operational parameters, and the possibility for on-line salt processing. Despite the advantages of a molten salt system, these concepts can also contain more complexity than many other energy storage systems due to the chemistry of the salt mixtures. In particular, molten salt systems can be particularly susceptible to corrosion. A risk assessment was performed as part of this dissertation, determining that corrosion risk is of particular concern in designing a molten salt system. To address the risk of corrosion in molten salt system design, two phases of research were conducted, which are described in this work. The first phase aimed to determine the effect of corrosion on the thermodynamic behavior of molten salt. In particular, the melting behavior of two types of molten salt was investigated, with additions of impurities that could result from corrosion. The second phase of research aimed to determine the effect of system design on molten salt corrosion. By use of COMSOL multiphysics, four different basic geometries were modeled, which were representative of geometries that could be found in a large-scale system. Molten salt laminar flow was modeled in these geometries, with corrosion behavior coupled to the laminar flow physics. This model was first of its nature and thus was simple in form. It provided information on the general impact of design changes on the velocity profile and corrosion behavior in representative geometries. The combination of experimentation and modeling determined that design changes can be made to reduce the impact of corrosion on a molten salt system. Extending the system temperature to above the entire melting range of a molten salt will ensure an operating fluid that is entirely liquid in phase. Modifying geometry to reduce areas of peak velocity will reduce the intensity of local corrosion, and reducing the overall system velocity will also reduce corrosion. Incorporating system design changes such as these in preliminary phases of design can reduce overall corrosion risk, extending the lifetime of the system.doctoral, Ph.D., Nuclear Engr & Industrial Mgmt -- University of Idaho - College of Graduate Studies, 2022-0
Predicting Vapor-Liquid Equilibrium Over the Entire Two-Phase Region Using Wagner Equation with Only Limited VLE Data
No full textThe predictive error relative to analytic values of entire-curve Wagner constants is studied for the reduced vapor pressures predicted by Wagner constants that are parameterized from a limited data interval. An algebraic solution for the fully-determined case based on only four data points is used to estimate the limited-data Wagner constants. First, seventy-two species are used to assess the impact of the location of the two interior points and the location and width of the limited-data interval upon the error in predicted Pv,r due to data imprecision. Hydrogen, helium, R152a, and water are used to assess error due to Wagner imperfection and compare predictive capability of the algebraic fully-determined and regressed over-determined approaches. Second, the repeatability/reproducibility of VLE data in the literature is studied by comparing reduced pressures calculated from Antoine constants applicable to a limited temperature interval with the entire-curve Wagner analytic values over the same limited-data interval. The entire-curve Wagner analytics are treated as “true” or “best” values and the Antoine analytic values as surrogate experimental data. Wagner constants for fifty-five species are subsequently estimated from the Antoine analytics for the fully-determined case, from which reduced vapor pressures below and above the interval are predicted and compared with the entire-curve Wagner analytics to estimate the ability of limited VLE data to be used to accurately represent the entire two-phase curve. The predictive capability of such limited-data Wagner constants is compared with that of the semi-theoretical Riedel and the empirical Ambrose-Walton equations. Lastly, reduced vapor pressures predicted from the standard and modified forms of the Riedel and Ambrose-Walton equations are used to parameterize the Wagner equation, again using the algebraic, fully-determined solution. The predictive power of such Wagner constants is compared to that of the underlying source correlations themselves. This is the first time the error of limited-data Wagner constants is segmented by interval location and width, between that due to data imprecision vs. equation imperfection, and fully- vs. over-determined solutions. Neither using a four-point, fully-determined solution rather than over-determination, nor using predictive correlations to supply “data” to a Wagner parameterization are instinctive approaches, and hence their novelty.doctoral, Ph.D., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 2017-1
Carbon Dioxide Enabled Methane Dehydroaromatization Reaction with High Stability
No full textBenzene has been found to be used in over sixty percent of all industrially made chemicals. However, with a societal desire to be less dependent on fossil fuels, this unknowingly hurts benzene production. Although there are other alternatives to making benzene, methane dehydroaromatization proves to be the most efficient option. There have been many studies about MDA, however, few studies have been conducted to show that gas additions can improve the reaction. One study went over the effects of a carbon dioxide addition within the gas stream. The study showed that carbon dioxide is in competing nature with methane but stabilizes the reaction to a small degree. The work conducted in this report is to give a more detailed account of how carbon dioxide affects the MDA reaction. Carbon dioxide can increase the reaction’s lifetime by over 700% (55-60 hours) but is most effective when its reaction time is held just above 20-25 hours (200% lifetime increase). With a carbon dioxide addition of 3 vol%, the reaction can keep a benzene selectivity of over 70% for its 25 hour lifetime. Of all the carbon dioxide values tested, 3 vol% addition provided the best results in terms of maintaining high conversion (~15%) and the highest selectivity (>70%). Carbon dioxide’s role was theorized to help stabilize the reaction by transforming methane into a more reactive species: methanol. Using temperature programmed desorption, it was also theorized that propyne is the main reactant in forming benzene. Propyne polymerization is a well known process, and it was theorized since propyne is the major product found on the catalyst’s surface that propyne polymerization occurs to create mesitylene. Mesitylene is then hydrocracked to form methane and benzene. Further investigations revealed that carbon dioxide has the properties of arc quenching. This allows it to absorb free electrons without altering its physical chemistry. It was finally theorized that with a 3 vol% carbon dioxide addition, the optimal ratio of oxygen addition to electron removal of the reaction can be achieved.masters, M.Engr., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 2021-1
Advances in Solvent Extraction: Separation and Purification of Adjacent Trivalent Lanthanides Using the Electroneutral Solvating Extractant N,N,N’,N’-Tetraoctyl Diglycolamide
No full textRare earth elements have become essential materials in advanced clean energy technologies and national security applications due to their unique properties. Despite their importance, the United States remains almost completely dependent upon foreign supply chains, notably imports from China, for both raw and finished commodities containing rare earth elements. This dissertation explores the implementation of a neutral ligand, N, N, N’, N’ tetraoctyl diglycolamide (TODGA), for the separation of rare earth elements. TODGA offers distinct advantages over traditional phosphonic acid extractants, notably the elimination of saponification to achieve high recovery in a solvent extraction circuit and improved adjacent lanthanide separation factors, ultimately requiring fewer solvent extraction stages to achieve high degrees of purity and recovery. This work marks the first use of TODGA’s unique chemistry to separate and purify the rare earths from each other in hydrochloric acid media using counter-current solvent extraction. Chapter 1 introduces the concept of rare earths as a critical material and highlights historic and future challenges associated with the rare earth supply chain. Separations remains as one of the greatest challenges due to high capital and operating costs to purify individual rare earth elements, thus emphasizing the need for advances in solvent extraction to enable a viable domestic supply chain in the United States. Chapters 2 and 3 provide background context that motivated the research by describing commercial rare earth separation processes and an overview of TODGA’s known applications and uses for trivalent lanthanide extraction and separation. While TODGA’s lanthanide extraction chemistry has been studied extensively for separations relevant to the nuclear fuel cycle, it has not been successfully applied in the field of rare earth mining and hydrometallurgy to separate individual lanthanides with high degrees of recovery and purity in a continuous counter-current solvent extraction cascade. TODGA exhibits a unique extraction trend among “light” low molecular weight lanthanides, with an observed 50% increase in adjacent light lanthanide separation factors as compared to the industry standard phosphonic acid PC88A. This suggests that a counter-current solvent extraction cascade with a reduced number of stages may be implemented for the purification of light rare earth elements. Chapter 4 outlines the various experimental methods that were utilized to conduct this research. A variety of techniques were utilized in the approach, including laboratory batch equilibrium solvent extraction experiments, counter-current mixer-settler testing, and process modeling and simulation using MATLAB/Simulink. Chapter 5 provides the rationale behind counter-current solvent extraction modeling and simulation for process design. Mass balances around a solvent extraction cascade may be written as a system of ordinary differential equations and coupled with empirical laboratory equilibrium data to model the approach to steady state. Alternative techniques for steady state cascade modeling using algebraic equations written in the form of a tridiagonal matrix and solved using the Thomas Algorithm are discussed. This approach may also be coupled with empirical expressions for calculating distribution ratios as a function of free TODGA and aqueous phase chloride concentration at equilibrium. Chapter 6 describes experimental results that were used to evaluate the feasibility of TODGA’s extraction chemistry in a counter-current solvent extraction circuit. While TODGA demonstrates improved light rare earth separation factors, they are still relatively low, implying that neighboring lanthanides essentially co-extract. Commercially, high degrees of purity and recovery are achieved by implementing a selective scrubbing technique through which the purified REE product stream is refluxed into the scrub section. Batch solvent extraction experiments and simplified counter-current solvent extraction experiments in mixer-settlers revealed that TODGA is indeed capable of selective scrubbing to purify REEs under proper solvent loading conditions. Chapter 7 describes the applied culmination of TODGA’s extraction chemistry through the design and experimental testing of a solvent extraction process to produce the permanent magnet precursor material didymium (75% neodymium and 25% praseodymium by mass), from a mixed light rare earth chloride feed representative of that produced from the processing of bastnäsite ore. The chapter includes single metal extraction data with empirically determined expressions for calculating distribution ratios, followed by batch counter-current extraction experiments for light REE separations. Batch experimental results were used to design a 24-stage counter-current solvent extraction cascade to purify PrNd from a mixture of La, Ce, Pr, and Nd. While experimental results of the cascade design did not achieve optimum recovery or purity, they indicate that TODGA can successfully be used to for the continuous separation and purification of light rare earths. Single metal distribution ratio correlations did not accurately model cascade behavior; a “pseudo single-metal” approach is presented to calculate distribution ratios under saturated loading conditions in a solvent extraction cascade. Chapter 8 discusses the implications of utilizing TODGA in an industrial setting. While the use of a neutral ligand has distinct benefits over phosphonic acids, there are several limitations to the solvent system that require additional research efforts to address. Furthermore, implementing TODGA chemistry has economic impacts that may potentially limit its commercial viability. Notable limitations discussed include organic phase loading capacity, ligand synthesis and production costs, and high molarity salt-bearing raffinate streams that must be recycled or disposed of. A structure/property relationship was identified for DGA extractants with varying alkyl chain substituents, indicating that short alkyl chains make stronger, more selective extractants but are prone to gelling and third phase formation. Longer alkyl chains maintain selectivity and slightly reduce overall extraction strength. Branched alkyl chains prevent gelling and third phase formation but comes at the cost of poor selectivity due to steric hindrance caused by the branched alkyl chains in the outer coordination sphere. Chapter 9 summarizes the general conclusion of this work: TODGA is capable of performing industrially relevant rare earth separations in continuous counter-current solvent extraction equipment, achieving high degrees of REE recovery and purity. However, its practical application is limited at this time due to its low organic phase loading. Ongoing research in collaboration with Oak Ridge National Laboratory is currently underway to synthesize and test novel DGA extractants with tailored alkyl chain substituents that achieve high degrees of organic phase loading capacity, maintain enhanced adjacent lanthanide selectivity among light rare earths, and demonstrate acceptable hydrodynamic behavior suitable for use in solvent extraction equipment.doctoral, Ph.D., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 2020-0
ANALYSIS OF TRANSIENTS AND CONTROL OF ADVANCED HIGH TEMPERATURE REACTOR-COUPLED HEAT EXCHANGERS SYSTEM
No full textControl of advanced reactor system consisting of a nuclear reactor, an intermediate heat exchanger (IHX), and a secondary heat exchanger (SHX) is investigated in this research. Initial transient analysis of the system was conducted using commercially available process simulation softwares PRO-II and DYNSIM. System parameters of significance – controlled and manipulated variables – were identified, and a control strategy was developed to maintain the controlled variables at their set points. The system response was simulated for various load disturbances, initially for the coupled heat exchangers system, followed by incorporation of the reactor dynamics in the system. Alternate strategies to control the temperature entering the process or power conversion unit (PCU) by either manipulating the secondary loop flow rate, controlling reactor power, or a combination of the two methods were investigated. Combining both methods of control showed great utility in controlling the temperature entering the process and may be an ideal method for control.masters, M.S., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 201
Capture of Radioactive Iodine and Krypton from Nuclear Off-Gas Streams with a Novel Sorbent
No full textReprocessing of used nuclear fuel (UNF) is key to making nuclear energy a sustainable, viable part of the world’s energy portfolio. However, during aqueous reprocessing of UNF volatile radionuclides are released in off-gas posing a hazard to health and the environment. Of these radionuclides, iodine 129 and krypton 85 present the biggest threat and are removal priorities. Since the 1960’s, many methods of removing iodine 129 and krypton 85 have been employed, including caustic and acidic scrubbing, fluorocarbon absorption, and cryogenic distillation. The problem with each of these processes is the use toxic and corrosive chemicals and high energy costs. Adsorption provides simpler, safer, and more cost-effective method of removal, and research into new materials for adsorption has been prolific. Nonetheless, much of the existing research is bereft of realistic studies at low concentrations, ambient temperatures, and with multiple components. To further this research, we have developed a novel adsorbent for iodine and krypton capture consisting of Engelhard titanosilicate-10 supported hollow carbon nano-polyhedrons (C/ETS-10), with large-scale synthesis and cost-effectiveness in mind. We investigated the capture of iodine and krypton on C/ETS-10 under single- and multi-component conditions, ambient temperatures, and concentrations similar to actual off-gas. Additionally, we developed a mathematical model based on mass-transfer to assist in scale-up of the process and compared it to the well-known Thomas, Yoon-Nelson, and Adams-Bohart kinetic models. Our investigation found that even in multicomponent conditions, 10 wt% C/ETS-10 has iodine capacity comparable to, and krypton capacity twice that of silver mordenite, a zeolitic sorbent considered to be at the forefront of sorbents for both iodine and krypton. Furthermore, the mass-transfer model fits experimental breakthrough curves better than the kinetic models and had inherent flexibility allowing extrapolation to other operating conditions. Overall, 10 wt% C/ETS-10 has proven to be a competitive sorbent for iodine and krypton at realistic off-gas conditions.masters, M.S., Chemical and Materials Science Engineering -- University of Idaho - College of Graduate Studies, 2017-0
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